1. Technical Field
The present invention relates to the salt-resistant Bacillus subtilis var. chungkookjang, accession number KCTC 0697 BP, derived from “chungkookjang”, a traditional Korean fermented soybean food, and to the poly-gamma-glutamic acid (or poly-gamma-glutamate, hereinafter referred to as γ-PGA) produced from said strain, which is an edible, soluble, anionic, and biodegradable polymer. In particular, the present invention relates to a novel Bacillus subtilis strain that produces an extracellular γ-PGA from an enzyme complex comprised of (1) D-amino acid aminotransferase EC 2.6.1.21, hereinafter referred to as “D-AAT”, which transfers the amino group of D-amino acids into keto acid, (2) glutamate racemase EC 5.1.1.3, hereinafter referred to as “GluRA”, and alanine recemase, hereinafter referred to as “AlaRA”, which catalyze the creation of isomers from alanine and glutamate, and (3) γ-PGA synthetase and γ-PGA produced from said Bacillus sp. strain.
As illustrated in FIG. 1, many enzymes participate in the synthesis of the γ-PGA.
2. Related Art
γ-PGA is a mucous polymer substance consisting of χ-glutamyl conjugated D, L-glutamate and is produced from Bacillus sp. strains separated from traditional fermented soybean foods, such as “chungkookjang” from Korea, “natto” from Japan, and “kinema” from Nepal. The γ-PGA produced from such Bacillus sp. strain is an edible, soluble, anionic, and biodegradable polymer (molecular weight: 100˜2,000 kDa), which can be applied as an absorption agent, hygroscopic agent, raw material for cosmetics, and in the manufacture naturally degradable plastic through the synthesis of ester derivatives.
Recently, many studies have been focused on the production and application of γ-PGA, especially in advanced countries. Thus far, researchers have actively attempted to develop materials to replace non-degradable polymers and produce heat-resistant plastic through ester reactions, soluble fibers, and membranes etc. In addition, the physical changes of γ-PGA caused by γ-irradiation have also been studied, along with the development and industrialization of hydrogels using bridge adhesives. For example, the composition of γ-PGA, the effects of Mn ions affecting the production of γ-PGA, uses for soluble polymers degraded by ultrasonication and low soluble plastic through the synthesis of ester derivatives (Biosci. Biotechnol. Biochem., 60(8): 1239–1242, 1996), and the production of γ-PGA in Bacillus subtilis and calcium dissolving agents as healthy food for treating osteoporosis (Japanese Laid-open Patent No. Hei. 6-32742) have all been reported. Moreover, the reduction of water contamination based on decreasing the phosphate content in water systems (European Patent No. 838160), a high ratio for making a gel through irradiation, hygienic products, including diapers prepared using a biodegradable adsorptive resin with a water-absorbing property, food, application in the horticultural industry (Japanese Laid-open Patent No. Hei. 10-251402), and it practical use (Japanese Laid-open Patent No. Hei. 7-300522, Japanese Laid-open Patent No. Hei. 6-322358) have also been disclosed. Furthermore, the uses of γ-PGA as a solidified biodegradable fiber or film and film-forming agent through dissolution, precipitation, and drying (Japanese Laid-open Patent No. Hei. 7-138364, and Japanese Laid-open Patent No. Hei. 5-117388), polymers for a drug carrier (Japanese Laid-open Patent No. Hei. 6-92870, Japanese Laid-open Patent No. Hei. 6-256220) have been reported.
Meanwhile, Korean studies, including the efficient production of γ-PGA (Korean Patent Application No. 1997-3404; Korean Patent Application No. 1997-67605) and the improvement of its physical properties have also been performed. While, Pacific Inc., a cosmetic company of Korea, produced γ-PGA from a Bacillus subtilis natto strain and used it as a raw material for cosmetics and other practical uses.